Radio frequency anechoic chambers are used to provide controlled repeatable environments for performing radio frequency radiation tests. Radio frequency anechoic chambers are meant to approximate an unbounded region of free space for electromagnetic waves and are meant to provide an environment in which radio frequency radiation tests can be made without introducing the errors caused by reflected waves or standing waves.
One type of test performed in radio frequency anechoic chambers is the measurement of power radiated from a piece of radio frequency equipment (termed the Equipment Under Test, EUT) as a function of polar and azimuth angle. Such a test allows a complete characterization of the spatial dependence of electromagnetic waves radiated by the EUT. The floor, ceiling and walls of radio frequency anechoic test chambers are tiled with radio frequency absorbers that are provided to substantially diminish reflections and standing waves. The EUT is supported away from the absorbing walls, ceiling and floor, usually in the center of the chamber, in order to make measurements. Elevating the EUT with a support also allows a measurement antenna to be moved so as to view the EUT from a wide range (nearly 180 degrees) of polar angle. To avoid large disturbances of the radio frequency fields emitted by the EUT, the support is made from dielectric materials as opposed to metal. However even a dielectric support perturbs radio frequency fields and can cause reflections that distort measurements made in radio frequency anechoic chambers.
One way to measure the level of unwanted reflections of radio frequency waves in an anechoic chamber equipped with an EUT support, and configured for measuring radiated radio frequency wave power as a function of polar angle, is to install a transmitting antenna that radiates uniformly as a function of polar angle (e.g., a horizontally oriented dipole) on the EUT support in the anechoic chamber and move a receiving antenna (also called a probe) over a large range of polar angles with respect to the transmitting antenna while measuring the power received by the receiving antenna. In an ideal radio frequency anechoic test chamber with an ideal support, there would be no variation in the measured field. The variation that occurs is termed “ripple”. The ripple can in part be caused by the support creating a disturbance of the radio frequency field emitted from the transmitting antenna.
In designing the support for the EUT, aside from the goal of reducing the disturbance of radio frequency fields in the anechoic chamber caused by the support, the support must also be made mechanically robust enough to support the EUT and all other equipment that is to be positioned with the EUT on the support. Achieving high mechanical robustness suggest that the support be made of thick section materials; however using thick section materials would tend to increase disturbance of radio frequency fields by the support. An additional requirement is that the support interfere as little as possible with movement of a receiving antenna in the anechoic chamber through a large range of polar angle with respect to the EUT supported on the support.
There is a need for a radio frequency anechoic test chamber with an EUT support, that meets the design criteria set forth above.